Browsing AuthorCelso

December 22, 2003

Verify Valid Domain

Use this code to verify if the domain part of an email address is valid:


use Net::DNS;

$email = "[email protected]";
(undef, $domain) = split (/@/, $email);
$resolver = new Net::DNS::Resolver();
$response ||= $resolver->query($domain, "MX")
  || $resolver->query($domain, "A");
defined ($response) ? print "$domain is valid"
  : print "$domain is invalidn";

It might also be a good idea to skip known domains, such as yahoo.com, google.com, etc.

November 18, 2003

Checking Regular Expression Syntax

If your program accepts a regular expression pattern, either from a user input or another module, you need to check that the pattern you receive is valid or not. To check for a valid pattern, apply the pattern against an empty string and wrap the expression in an eval.


sub my_func {
    my ($pattern) = @_;

    eval {
        "" =~ $pattern;
    };
    if ($@) {
        die "Something wrong with your pattern: $pattern";
    }

    # Otherwise, pattern is good and use it here.
}

August 27, 2003

How To Determine Installed Modules

Here’s how to determine what modules have been installed after the original Perl installation, hence showing those modules not part of the core installation. Type this from a command line:


perldoc perllocal

August 13, 2003

How To Tell A Number From A String

Often, I need to compare two variables but I don’t know if they are numbers or strings. I need to know the type so I can pick the proper comparison operators, i.e., == or eq, > or gt.
So, here’s how to do it:


~$x ne ~"$x" ? 'numeric' : 'string'

~ is the bitwise negation operator (see perlop). It does not negate integers and strings in the same way.

Examples:


$ perl -e 'print ~1, "n"'
4294967294
$ perl -e 'print ~"1", "n"'
Œ

(character which ASCII code is 255 – ord(‘1’))

June 21, 2003

Create Dir Path

To create a directory path programatically:


use File::Path;

mkpath "/usr/local/apache/htdocs/articles/2003";

This will create the 2003 directory and all parent directories as needed. This is the same as mkdir -p command.